Last night, I was tightening the tension on my Jet 14″ band saw, and I heard a loud “SNAP” right inside the tension adjuster. The tension meter dropped to a reading of 0. After that, no matter how much I turned the tension knob, the tension would not move.
I opened up the whole tension mechanism (removed everything and cleaned it out). I examined the spring. It doesn’t look broken or anything. It just looks kind of “stretched out” — not as tightly wound as it once was. It seems as though it should still be able to tighten up with the tension knob, but…alas, it does not.
I’ve never experienced a broken band saw spring. Actually, I’ve never experienced a broken anything on my band saw.
Is my spring shot? Or is there another possibility?
Edited 9/5/2003 8:41:28 AM ET by Matthew Schenker
Replies
Matthew,
On most bandsaws the spring is under compression, it is being crushed not stretched when the tension is increased, so it wouldn't snap if it failed.
I suspect that the square nut that the spring rides on has stripped out, it is about the only failure I can think of that wouldn't be obvious when you took the mechanism apart.
Actually I can think of one other possibility, did the tip of the long threaded tensioning screw drill through the cast iron of the saw's frame and drop into the space below?
John W.
John,
Thanks for your reply.
The tension rod has not drilled into the cast iron of the housing, although I have noticed lately that some black filings are collecting on the housing below the threaded rod. When I saw these filings, I suspected that the rod might be burrowing into the housing, but I still had a clearance of about 1/16" between the rod and the housing.
How would I tell if the square nut is stripped? Looking at it, it doesn't look bad. I can still thread it up and down the tension rod. But when I try to turn it when it's installed in the tension assembly, it doesn't tighten the spring.
But I see what you mean. Looking inside the tension assembly, there isn't much else that could go wrong. It's either the nut or the spring.
Well, I did think of one other thing that might go wrong. On the Jet 14", the housing that secures the square nut is aluminum. Could this eventually wear out, making it so that the nut does not have a tight enough housing? The loud "SNAP" I heard could have been the sound of the square nut slipping inside the aluminum housing. Problem is, I do not know what the nut is supposed to look like inside the housing, since I did not open up the assembly when I first bought the saw. Maybe the housing is damaged? If this is the issue, then I think I have a major problem on my hands!
Maybe it's time to check my warrantee!
Edited 9/5/2003 9:46:54 AM ET by Matthew Schenker
Matthew,
The nut is a loose sliding fit in the square housing, it would have to be worn round to be slipping and there is no reason why either the nut or the housing would wear appreciably. If the nut were failing, it could be the source of the filings you saw where the rod bears on the frame. The bottom of the rod should actually be touching the frame, just where is that 1/16th of an inch clearance that you refer to?
Even if the spring failed completely the nut could push on the spring and force the housing upward creating tension on the blade, so a spring failure alone wouldn't create a situation where you couldn't tension the saw blade.
If the nut were stripped it, would probably still thread up and down the rod on the little bit of remaining threads, but they wouldn't hold under the resistance of the spring.
The fact that the nut doesn't move when you rotate the handle after you have assembled the unit seems to indicate a stripped nut. If the threads were there, the nut would have to move when the rod turned. ( Is the rod actually turning?, you could have a loose handle that slips under load, the snapping sound could have been the the rod shearing off inside of the hub of the handle.)
The rod itself could also be stripped but the damaged threads would be fairly easy to see. If you replace the nut, you should also replace the rod since it is probably worn also. For a quick fix, you could try to find a replacement nut at a hardware store, but it may be hard to locate a square nut with a metric thread, though it is possible that the threads are inch size. Lubing the replacement nut and rod with a little grease will extend their life greatly.
John W.
John,
Thanks for your very informative reply. I checked again, and the tension rod is seated firmly in the handle, so the snapping sound did not come from the rod slipping inside the handle. I also checked the threads of the tension rod, and they APPEAR to be OK. The aluminum housing of the tension box seems to be fine -- no scratches or cuts or anything. I also checked the bahavior of the nut again. Yes, it moves up and down the threaded rod when I am spinning it with my fingers, but when I install the tension box and try to tighten it with the handle, the rod just spins and the spring does not compress at all. So, it looks like the nut is the most likely culprit here.
Luckily, the nut is probably the cheapest part to replace. I am going to see if I can find one of these nuts. I'll also tae your advice about lubricating the nut and rod.
I will admit that my band saw had been sitting unused for over a month. Perhaps this has something to do with it.
My tension rod has a slight clearance between its tip and the cast-iron housing. I always thought this was the way it is supposed to be. I wonder if this band saw was set up wrong from the factory. Since it was my first band saw, I never questioned this...
I'll tell you what I discover when I install the new nut.
Again, thanks for your wonderful help.
Well, I consulted with a tool shop today, and it looks like the tension rod AND the nut are both shot to heck. I couldn't even unthread the nut!
I just ordered a new tension rod and a new Iturra spring to replace the old rod and spring. I got mine from Highland Hardware.
What a bad week this has been. Something wrong with my SCMS -- and now this! What will happen next!
Edited 9/5/2003 2:40:43 PM ET by Matthew Schenker
Just some info on the Jet BS and Iturra spring combo. I have a 14" Jet 3 speed BS that I use for site work. It's junk as it comes from the factory. The motor and the replacement fried within hours. The tension spring collapsed and the rod bored a hole in the frame. The upper wheel was egg shape.
Installed a unstallable 1hp motor from a 1942 Unisaw. Can resaw 10" maple like a hot knife in butter. Installed the Iturra spring but only tension the blades to about 1/2 the normal tension on the scale. I use Suffolk low tension blades. The Jet BS frame can't handle the tension from the Iturra spring. Measure the distance from the bottom of the guides to the table without tension, then check it with reccamended spring tension. I'm not saying the Iturra is bad, it's a better spring than Jet's but the saw will not handle the constant high tension if you use high tension blades.
With the high tension spring, the rod will bore a hole in the frame. This can be corrected by installing a grade 8 bolt in the frame so the rod will turn on the bolt head or put grease in the hole where the rod turns in the frame.
Dave Koury
Edited 9/6/2003 8:51:46 AM ET by DJK
DJK,
You can say that again!
I just received my new crank and Iturra spring from Highland Hardware and installed them in the band saw. The spring has so much tension that it maxed out my wheels (the top wheel raised so high it hit the wheel cover) before it even registered on the scale. In other words, its got so much tension I can't even use the built-in tension meter!!!
I'm going to call Highland Hardware tomorrow. I DO NOT WANT TO BUY A TENTION METER!!!!!
Contact Louie Iturra directly, he's a wealth of onformation, and has a catalog that is better than most bandsaw "how to" books you might purchase.
Time to be a cynic... Even if that is possible around here...LOL
Some thing may not be right..
Wrong replacement parts.
And the infamous - I know I put it back together right.
Who ever invented work didn't know how to fish....
Matthew,
Something isn't right here, no matter how stiff the spring was it wouldn't create the problem you're having, so buying a tension meter won't solve your problem. I've installed Iturra springs on six or eight saws over the past few years and never had the problem you're describing.
Possibilities: Are you sure you have the right length blades, too long a blade would create the problem you're having. Was the blade fully on both wheels? Was the square nut sliding easily inside of the tensioner housing or was it turned forty five degrees so that it was bearing against the bottom of the housing instead of sliding up inside of it?
I'd suggest that you get a book on bandsaw maintenance or some of the back issues of Fine Woodworking that discuss bandsaw tuning and operation, I really think they would help you out.
John W.
John,
Thanks for your persistence! Boy am I embarassed. The problem is I had a momentary lapse of reason. I recently purchased a riser block for my band saw, and when I had that problem with the spring, I decided to take everything apart and clean it out. While doing this, I was thinking, "This is a good time to install that riser block." But I didn't actually do it. Later, when I was putting everything back together, with the Iturra spring and the new crank installed, for some reason, I imagined that I actually installed the riser block. With this in mind, I went ahead and loaded up a 103" blade instead of the regular 93.5" blade. What a wacky mistake -- I remember looking at it and asking myself why it looked different...
Needless to say, I could tension that thing all day without getting it tight.
My only excuse is that I did this at 11:00 at night. I usually have a cut-off of 9:30 PM in the shop -- for good reason apparantly.
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